There is an intimate interrelation between principles and procedures in classification, and modern work in this field has been profoundly affected by the development of electronic computers. Besides the delineation of natural systems and the achievement of economy of memory and ease of manipulation, the primary purpose of classification is the description of the structure and relationship of groups of similar objects. Successful classifications generate scientific hypotheses, although much classificatory work has applied, practical goals. The acceptance of polythetic taxa is a major conceptual advance and has directly led to classifications based on many, equally weighted characteristics. The specification of data for classification by computer will enhance objectivity but not eliminate cultural and subjective biases. Techniques of classification include cluster analysis and ordination, and numerous ways of representing classifications have been elaborated recently. By the application of graph theory to some classificatory problems it has been possible to reconstruct evolutionary branching sequences. Computer classification has been successfully applied across a broad range of disciplines.